The present invention relates to rock reinforcing systems and, more particularly, to roof bolting methods and apparatus wherein a bolt is tensioned by threading into an anchor which is secured within a drill hole by resin grouting.
Among the various types of mine roof support systems employing rock bolts anchored in bore holes are the purely mechanical or point-anchorage systems, the resin grouted systems, and combinations of the two wherein the bolt is tensioned by threading into a separate member which is anchored in the drill hole by resin grouting. In the usual mechanical anchorage systems an expansion anchor is placed on the threaded end of the bolt prior to insertion into the bore hole. As the bolt is advanced, the anchor expands to grip the inner surface of the drill hole and the bolt may be tensioned to the desired degree by applying sufficient torque. Although resin grouting systems wherein the bolt is anchored directly by a hardened resin mixture offer certain advantages, the bolt cannot be tensioned once the resin has set.
More recently roof support systems have been proposed wherein the advantages of the mechanical and resin anchorage systems are combined. Such systems are typefied by U.S. Pat. Nos. 3,877,235 of Hill and 4,051,683 of Koval, among others. In these systems an internally threaded member such as a nut or hollow collar is anchored within the drill hole by the resin mixture and the bolt is tensioned by threaded advancement into the anchored member. Stop means are provided to limit advancement of the bolt into the threaded member as the assembly is rotated to break the resin cartridge and mix the contents thereof. After the internally threaded member is anchored by the resin the stop means is fractured by application of sufficient torque to the bolt, which may then be tensioned to the desired degree.
While such systems are generally satisfactory for the intended purpose, there remains the possibility of malfunction due, for example, to premature fracture of the stop means which limits initial advance of the bolt into the internally threaded member as the resin cartridge is broken and its contents mixed. Also, since the bolt is assembled with the threaded member and elongated bar affixed thereto prior to insertion into the drill hole, the length of the total assembly is often too great to allow use thereof in confined spaces such as so-called "low coal".
It is a principal object of the present invention to provide novel and improved methods and apparatus for supporting a mine roof, or similar rock formation, by means of a tensioned bolt threaded into a resin anchored member within a drill hole.
A further object is to provide an anchoring assembly including an internally threaded member for receiving a rock bolt together with a removable installation tool for use in securing the assembly in a resin grouting.
Another object is to provide a method and apparatus for installing a mine roof bolt which can be employed in more confined spaces than similar prior art systems.
Still another object is to provide a mine roof support system wherein a rock bolt is tensioned by threaded advancement into a member anchored in resin grouting which requires no means for limiting initial advance of the bolt and requiring application of excess torque after the resin sets.
Other objects will in part be obvious and will in part appear hereinafter.